A significant movie? (4)
I believe the answer is:
omen
'a significant movie?' is the definition.
The answer and definition can be both related to communication as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
This is all the clue.
Can you help me to learn more?
(Other definitions for omen that I've seen before include "Auspice" , "Prognostication" , "Portent of things to come" , "Sign of something to come" , "Harbinger, prophetic sign" .)